The TIM gene family was identified using a congenic mouse model in which polymorphisms in TIM-1 and TIM-3 wre associated with Th1-Th2 differentiation and allergen-induced ainway hyperreactivity (AHR) between BALB/c and congenic HBA mice. The long-term goals of Project 3 are to understand how the Tim genes regulate peripheral tolerance, adaptive immune responses, and allergy. In the previous grant period we showed that TIM-1 is an important costimulatory molecule for T cells, that TIM-1 and TIM-4 modulate T cell responses and the development of tolerance, and that TIM-1 and TIM-4 are receptors for phosphatidylserine (PtdSer), a key molecule for recognition and uptake of apoptotic cells. We have found that TIM-3, expressed on Th1 cells and APC, is also a receptor for PtdSer and that the allelic variants of TIM-3 associated with asthma differ in their recognition of PtdSer. These results together suggest a new paradigm for TIM proteins as PtdSer receptors that by regulating the recognition and clearance of apoptotic cells, can regulate tissue homeostasis, T cell responses and the induction of peripheral tolerance. In Specific Aim 1 we will determine the mechanisms by which TIM-4 expressed on APC, and TIM-1, expressed on activated T cells and Th2 cells, regulate oral tolerance and prevent food allergy. We will examine mechanisms by which TIM-4 blockade inhibits oral tolerance induction. In Specific Aim 2, we will characterize the cell types and APC subset(s) in the lamina propria and mesenteric lymph node that express TIM-4, the conditions that modulate expression of TIM-3 and TIM-4 following exposure to danger signals such as bacterial products that initiate food allergy. We will examine the consequences of T cell interaction with TIM-expressing APC on T cell subset differentiation. In Specific Aim 3 we will investigate the role of TIM-3 polymorphic variants, which we have recently shown differ in recognition of apoptotic cells, in modulation of immune responses in BALB/c and HBA mice, and determine the roles of TIM-1 and TIM-3 in modulating the development of airway hyperreactivity in these strains. We have developed unique reagents that will enable us to accomplish these goals. We have generated panels of anti-TIM-1 and TIM-4 mAbs, we have generated TIM-4 and TIM-1 transgenic mice, and TlM-1 deficient mice are now breeding in our colony. Our laboratory has extensive experience in the study of tolerance as a mechanism that protects against Th2-driven immune responses and in the study of dendritic cells (DCs) and antigen-specific CD4+ Tpeg cells. These studies will greatly improve our understanding of immune regulation and lead to new therapies for inflammatory diseases.